Web heat treatment and apparatus therefor



Aug. 1, 1961 A. v. ALEXEFF ET AL 2,994,133

WEB HEAT TREATMENT AND APPARATUS THEREFOR 2 Sheets-Sheet 1 OriginalFiled Sept. 17, 1954 @235 XANDER v AL Msuns 2R8 HPCAARDS A. v. ALEXEFFET AL 2,994,133

WEB HEAT TREATMENT AND APPARATUS THEREFOR Original Filed Sept. 17, 1954Aug. 1, 1961 2 Sheets-Sheet 2 FIG. 3

FIG. 4

F G 6 INVENTORS ALEXANDER V. ALEXEFF EDWIN P. HONBURG HOWARD RICHARDSwid rates 2 Claims. (Cl. 3456) The present invention relates to heattreatment of webs and strands and particularly to method and apparatusfor attaining very precise and responsive temperature con trol of thetreated material. For purposes of this application strands is to beunderstood to include monofilaments such as nylon, rayon, and glassfiber as well as wires, cords, narrow tapes and tubings, and strips" isto be understood to include strands and also webs such as metal sheet,paper, textiles, films and wide tapes.

In a multitude of present-day continuous or semicontinuous processes forthe heat treatment of strip, it is necessary to maintain the treatedmaterial within critical temperature limits during the actual heattreating step (usually while also maintaining a certain time of exposureor at least not departing from a certain range of exposure times). Anyvariables which tend to displace strip temperature across such criticallimits must, therefore, be counteracted by adjustment of the rate ofheat transfer to the web. Such adjustment is accomplished in a number ofways. For example, oven temperature is varied by increasing ordecreasing the output of the burners or heating elements which are thesource of the heat. It will be apparent that close strip temperaturecontrol under quickly fluctuating control conditions cannot bepractically attained with this rudimentary arrangement. Anotherprocedure is to provide a standby supply of heat (i.e., heated air)which can be supplied to the oven or drier on demand. Conversely, anoverheated oven may be provided which is cooled to the desiredtemperature by outside air or other cooling medium, the rate of supplyof the cooling medium being varied in response to control requirementsto counteract any tendency of the strip to exceed temperaturelimitations. Thus, a degree of strip temperature control may be attainedby responsively and continuously damping into the oven or drier anaccumulated heating or cooling medium. However, the inherent waste andexpense of this procedure renders it impractical for close temperaturecontrol. If a relatively wide temperature range is allowed, damping inof the alternative supply used occurs only relatively infrequently, butfor close control damping in of the alternative heating or coolingmedium must occur almost continuously, representing a prohibitive heatloss. Another possibility is to vary web speed, but in most productionset-ups to continuously vary speed of the processing line is obviouslyimpractical. The variation of web speed is, of course, entirelyinapplicable to operations in which time of exposure must be maintainedat a given figure or within a narrow range.

The above considerations have limited the possibilities of many stripheat treating processes where the ideal would be to closely approachcritical temperature without exceeding it. Commercially attainable endresults are compromised by the fact that the ideal is attainable only bythe use of prohibitively costly and wasteful methods. For example, inhot stretching of nylon fabric following coating or impregnation, it isdesirable to approach as closely as possible the limiting top webtemperature at which the fabric will soften and fail or scorch.Conventional hot stretch installations provide 72,994,133 Patented Aug.1, 1961 elaborate temperature control means for the oven through whichthe web is to pass. As control conditions vary (the wide variable isusually web speed which, on a continuous line, is adjusted from time totime according to production demand) it is, of course, necessary to varythe oven temperature. Excessive destruction of material duringshutdowns, either by overheating or under treatment of portions of theweb, must also be avoided. Highly responsive control of web temperaturecannot be achieved without completely prohibitive expense due to heatwaste and the cost of large auxiliary equipment. Accordingly, compromiseis necessary and a considerable margin of safety must be maintained bychoosing operating conditions so that the web temperature is well belowthe critical value which it can stand, despite the desirability ofclosely approaching this critical value.

An object of the invention is to provide close control of striptemperatture during heat treatment, such close control being readilymaintained despite rapid fluctuation of control conditions such as stripspeed, temperature and humidity of the input side of the strip, ambientair temperature and humidity and any other variables that tend to affectstrip temperature during the heat treating step.

Another object of the invention is to make possible a very close controlof the amount of stretch of a strip in a continuous or semi-continuousprocessing operation. In many applications close control of striptemperature is not, in itself, of primary importance, but it is highlydesirable that the amount of stretch of the strip be confined withinnarrow limits. The amount of stretch is generally a function of threevariables: strip tension, heating period and strip temperature. Thefirst two of these, strip tension and the time of exposure of the strip,

may be very closely controlled by conventional methods.

Heretofore, however, the third of these variables, strip temperature,has not been subject to such precise control. Accordingly, anotherobject of the invention is to make possible extremely close control ofthe amount of stretch of a strip on a continuous processing basisthrough precise control of the several parameters of the amount ofstretch.

Another object of the invention is to provide improved means ofcontrolling strip temperature regardless of whether extremely finecontrol is required.

Another object of the invention is to provide for quick accommodation ofdesired changes in strip speed without the necessity of varying oventemperature.

Another object of the invention is to resolve, by radical and simplemeans, certain problems of heat damage or improper treatment of thestrip incident to shutdown.

A further object of the invention is to provide for economicaltemperature control in continuous or semicontinuous processes over anindefinitely broad range of strip speeds by employing gangs of ovens oroven sections which may be by-passed and completely shut down when notrequired.

These and other objects and advantages of the invention will becomeapparent from the following description of specific embodiments of theinvention. As will be apparent to those familiar with Web or strandprocessing, specific mechanical, electrical or hydraulic equipmentcomponents to be employed in any given installation are a matter ofchoice within the routine skill of the art. Suitable components in eachillustrated embodiment are, therefore, illustrated schematically in theinterest of clarity in order that the invention itself may be mostconcisely and completely disclosed and understood.

In the drawings:

FIGURE 1 illustrates a relatively refined continuous web processingsystem employing the invention.

FIGURE 2 illustrates a semi-continuous web processing system employingthe invention in a somewhat different manner than it is employed in theapparatus shown in FIGURE 1.

FIGURE 3 illurstrates an alternate set-up which may replace the centralportion between the lines C-C and D-D of the processing line shown inFIGURE 2.

FIGURE 4 illustrates an alternate set-up which may replace the centralportion between the lines AA and B-B of the processing line shown inFIGURE 1.

FIGURES 5 and 6 illustrate alternative oven and dancer arrangements.

FIGURE 1 illustrates a fully continuous web treating installationinwhich the invention is employed. The illustrated installation might beemployed for impregnation and coating :1 web of nylon fabric with aplastic which is applied to the fabric in a dipping operation, the webthen being heated, dried, and simultaneously stretched underconsiderable tension. In such hot stretching it is desirable to approachas closely as possible the upper temperature limit at which the fabricwill fail or permanently weaken. In the illustration the web isindicated by the reference numeral 10.

The main components of the installation shown in FIGURE 1 comprise apair of let-0E stands 11 and 12, a splice press 13, a tensionestablishing drive stand 14, a let-01f accumulator 15, a dip station 16,a first hightension-capacity pull rod stand 17, a vertical drying oven18, a tension sensing stand 19, a second high-tensioncapacity pull rollstand 20, a wind-up accumulator 21 and a pair of wind-up stands 22 and23.

The installation may employ in any conventional manner a plurality ofvariable speed DC. motors as a power and control means for the severalweb driving members. The power and control system may comprise a motor28, generator 29, field exciter 30, an overriding or governing speedcontrol rheostat 31, and a plurality of voltage responsive variablespeed DC. motors 32, 33, 34, and 35, each of these motors with theexception of the motor 33 being provided with its own subsidiary speedcontrol means such as field voltage rheostats 37, such several controlmeans being responsive to variation in tension at several points in thesystem as explained below. A speed reducer 36 associated with each ofthe motors is mechanically linked with one of the processing linecomponents as indicated in FIGURE 1.

The drying oven 18 may be constructed and arranged so that both entranceand egress of the web occurs through the port 42 during normaloperation, the web being guided into and out of the port by the rolls41. Within the oven the web passes around a dancer roll 40. The dancerroll 40 is mounted for lateral displacement so that it may be shifted upor down in a vertical path within the oven 18 and may furthermore belowered a sufiicient extent to pass completely or at least partially outthrough the port 42. For this purpose the ends of the dancer roll 40 maybe mounted in blocks which are engaged by an endless cable or chain 43at either side of the oven. Each cable or chain 43 passes aroundassociated sprockets or sheaves 44, one of which is powered by areversible motor 45 through a speed reducer 48. It will, of course, beunderstood that other equivalent mechanism may be employed to shift thedancer roll 40, the choice of the most desirable mechanism being amatter of mechanical expediency in the particular circumstances andconditions.

In this example of the invention, a web temperature detector in the formof a radiation pyrometer 46 is provided to sense web temperature at theoutput end of web travel through the drying oven. Through a suitable andconventional control potentiometer 47 the motor 45 is controlled inresponse to sensed temperature so that upon increase in temperature thedancer roll 40 is lowered and upon decrease in temperature the dancerroll 40 is raised.

The overall speed of the processing line shown in FIG- URE 1 is governedby the pull rolls 17. It will be seen that the speed of the motor 33associated with these pull rolls is governed directly by the overridingcontrol rheostat 31, there being no ancillary variable control for thefield voltage in this motor 33. As is conventional, variation of thearmature voltage for this motor correspondingly varies armature voltagein the other drive motors 32, 34 and 35 through the common armaturevoltage line 50.

When the web processing line is running under normal conditions, arelatively low tension is maintained between one of the letoif stands 11or 12 and the tension-establishing drive stand 14 by simple brakefriction on the letolf stand. Between the drive stand 14 and thehigh-tension capacity pull rolls 17, an intermediate tension ismaintained by the normally extended letoff accumulator 15 which has aweight or tension member W exerting a constant force in tension on thefestooned web within the accumulator. Shifting of the lower member ofthe accumulator controls the associated rheostat 37 through a linkage55. Thus, as the lower member of the accumulator tends to rise, therheostat is automatically adjusted through linkage 55 to cause the motor32 to speed up, which, in turn, tends to free the accumulator causingthe lower member of the accumulator to move downward. Thus, a feed backor self-governing control maintains a constant length of web between thedrive stand 14 and the pull rolls 17.

When the letoff roll of webbing is about to become exhausted, the motor32 is stopped, by suitable means such as a cut-off switch, causing theweb to be locked at the drive stand 14. When this occurs, the lowermember of the accumulator 15 proceeds to rise as webbing is pulled alongby the pull rolls 17. However, constant tension is maintained by theexistence of the weight or tensioning member W. During exhaustion of theletoff accumulator 15, the alternate fresh letolf roll from one of theletofl stands is spliced to the tail of the nearly exhausted web at thesplice press 13. Thereupon the web, at the drive stand 14, is unlockedby cutting back into the circuit the motor 32. The lower bar of theletoif accumulator is now in an abnormally high position, and,accordingly, the linkage 55 controls the rheostat 37 so as to call forgreatly increased speed of the motor 32. Thus, the accumulator 15quickly refills, and, as its lower member approaches its normalposition, the rheostat is automatically varied through linkage 55 untilthe speed of the motor 32 is reduced to its normal range, whereuponnormal feed back or self-governing control of the motor speed continueswithin such normal range.

During passage from the drive stand 14 to the pull rolls 17, the webbingis illustrated as being processed at the dip station 16, the webbingbeing dipped into a coating liquid 56, then passed between scraper bars57, squeegee rolls 58 and heater bars 59.

Between the pull roll stand 17 and the second pull roll stand 20, arelatively high tension, which may be in the order of several thousandpounds, is maintained in the web by a weight or tensioning spring orother equivalent member W associated with the tension-sensing stand 19.Any tendency of the tension through this portion of the run to fall offor build up causes shifting of the member W, which, in turn, through itsassociated linkage 51 and rheostat 37, speeds up or slows down the motor34 until the member W is returned to its initial position.

Relatively low tension is maintained between the pull roll stand 20 andthe wind-up stands 22 and 23 by the control associated with the wind-upaccumulator 21, this control governing the speed of the wind-up standsand being similar to the control of the drive stand 14 by the letofIaccumulator 15, except that the lower member for the wind-up accumulatoris normally in raised position. When a wind-up stand is filled, themotor 35 associated with that stand is stopped and the guide rolls 53are locked together. When this occurs the lower member of theaccumulator 21 proceeds to fall as webbing continues to be supplied toit by the pull roll stand 20. Constant tension is maintained between theweight or tensioning member W associated with the wind-up accumulator21. During fill of the wind-up accumulator, the web is severed on theoutput side of the rolls 53 and the alternate wind-up stand is threadedwith the webbing, the rolls 53 being either manually advanced or beingadvanced by a small auxiliary motor a slight amount to permit suchthreading. Thereupon, the guide rolls are unlocked while Simultaneouslythe motor 35 is cut back into the circuit. The lower member of thewind-up accumulator is now in an abnormally low position and,accordingly, the associated linkage 52 controls the associated rheostat37 so as to call for greatly increased speed of the motor 35. Thus, theaccumulator 21 quickly empties, and as its lower member approaches itsnormal raised position, the rheostat is automatically varied throughlinkage 52 until the speed of the motor 35 is reduced to its normalrange, whereupon normal feed back of self-governing control of the motorspeed continues within such a normal range.

When the line is operating at speed as determined by the overridingcontrol rheostat 31, temperature of the web is sensed by the radiationpyrometer 46. As temperature starts to increase or decrease, the motor45 is controlled to lower or raise the dancer roll 40. It will beunderstood that the temperature within the oven 18 may remain almostconstant, varying only slightly according to ambient conditions oftemperature and humidity. Even such minor changes are compensated for bythe control of the motor 45 by the pyrometer 46. Thus, it is possible tocontinuously operate at a web temperature which approaches very closelycritical web temperature. If it be comes desirable to change web speed,the setting of the rheostat 31 is varied. As the changing speed beginsto reflect itself in a change in web temperature, the pyrometer 46automatically causes the motor 45 to change the position of the roll 40in a direction to overcome the indicated direction of change of webtemperature. I

It will be observed that while sensing of the temperature of the webitself approaches the ideal control, there may be other variables whichare straight line or other known or determinable functions ofwebtemperature. Accordingly, it is possible to provide for sensing ofsuch variables rather than providing for direct sensing of webtemperature. For example, in some installations Web temperature may veryclosely follow oven temperature and thus, sensing of the oventemperature may provide for satisfactorily accurate control of webtemperature.

It will be apparent to those familiar with web or strand processingtechinques and equipment that the electric power and control means maybe replaced by conventional mechanical or hydraulic apparatus, and thatthe specific supports shown may be varied as a matter of expediency toprovide for greater range control, more eflicient drives, greaterpracticality of the circuit under given conditions, or for otherpurposes, all as is conventional in the art.

In FIGURE 2, a semi-continuous installation embodying the invention isillustrated. This installation may include a let-off stand 111, a splicepress 113, a dipping station 116, a high-tension-capacity pull rollstand 117, a vertical drying oven 118, a tension sensing stand 119, asecond high-tension-capacity pull roll stand 120, which includes tensionsensing elements and a wind-up stand 122. It will be seen that theprocessing line illustrated in FIGURE 2 is generally similar to thatshown in FIG- URE l, with the exception that no accumulators areprovided so that change-over of the letoff and wind-up rolls cannot beaccomplished without shutting down the line. Relatively low tension fromthe stand 111 to the stand 117 is maintained by brake friction at thestand 111. Through a tension sensing element 126 and a suitable linkage124 associated with the stand 120, the motor 127 is controlled tomaintain correct tension at the output end of the line.

Also, tension between stands 117 and 120 is maintained by the feedbackcontrol from the tension sensing stand 119 in a manner which will beapparent from the drawings and is in all respects similar to thefeedback control to the tension sensing stand 19 in FIGURE 1. In theinstallation shown in FIGURE 2, positioning of the dancer roll isaccomplished by remote control of a motor which, through a speed reducer148, raises or lowers the dancer roll 140 by a linkage including thesheaves 144, such linkage being similar to the linkage which includesthe sheaves 44 in FIGURE 1. The remote control means for the motor 145is indicated in FIGURE 2 as a reversing switch 147.

In the installation shown in FIGURE 2, the speed of the line as a wholeis tied in to the position of the dancer roll 140 through the linkage146 and armature voltage rheostat 149. Fine web temperature control isnot accomplished in the sense that it is attained in the installationshown in FIGURE 1, that is, varying ambient conditions are not accountedfor. However, very rapid changes in web speed may be accomplishedwithout disturbing web temperature and while maintaining constant oventemperature.

When it is desired to shut down the line, the dancer roll 140 may belowered throughout the length of the oven 118, thus progressivelydecreasing web speed while at all times maintaining proper webtemperature. The dancer roll 140 may thereupon be lowered finallythrough the port and the line may be simultaneously stopped. Thus, inchange-over wastage due to improper heat treatment of certain portionsof the web is avoided and, at the same time, constant oven temperaturecan be maintained.

It will be understood that a control set-up similar to that illustratedin FIGURE 2 may be employed on a fully continuous line such as thatshown in FIGURE 1. While the control illustrated in FIGURE 2 is not asrefined as the control originally described in connection with FIGURE 1,it will nevertheless enable substantial economies to be realized in theoven installation, while still making possible rapid changes inproduction.

FIGURE 3 illustrates a modification of the equipment shown in FIGURE 2,the portion of the equipment between lines CC and DD in FIGURE 2 beingreplaced by the apparatus shown in FIGURE 3. The single oven 118 isreplaced by a multiple oven or a plurality of ovens 118A, 11813, and118C, each having its own dancer roll 140A, 14GB, and 140C. Each ofthese dancer rolls is positioned by control means similar to thatassociated with the dancer roll 140. Through linkages 146A, 146B, and146C the position of these dancer rolls controls the heating of seriesconnected armature voltage rheostatsr 149A, 149B, and 149C. As a runcommences, the dancer roll 140C is raised in the oven 118C. When theroll 140C has reached its top-most position, the roll 140B is thenraised, then in turn the roll 140C. With decreasing speed, the rolls arelowered in reverse sequence from their ovens, the roll 140C beingcompletely withdrawn from its oven upon complete shutdown. In theparticular installation shown, it is immaterial which roll is raised orlowered first. It will be apparent, however, that it may be desirable tointer-lock the controls so that raising or lowering of the rolls willhave to progress in a definite sequence. It might be desirable tomaintain the oven 1180 at temperature, thus at all times maintaining theline in condition to commence or continue operation at one-third of itsfull speed capacity. The other chambers might be brought to temperatureonly when higher capacity was called for. FIGURE 4 illustrates amodification of the apparatus shown in FIGURE 1, the specific apparatusshown in FIGURE 4 replacing the portion of FIGURE 1 between the lines AAand B-B. In FIGURE 4, next to the oven 18, is provided a cooling tower70. The linkage which raises and lowers the dancer roll 40simultaneously and conversely lowers or raises a dancer roll 71 Withinthe cooling tower. The control of the position of the dancer roll 40 ismanual and is accomplished by the motor 75 acting through a speedreducer 76, the motor being controlled by an on-and-off reversing switch77. It will be apparent in this example that Web temperature must bevaried manually with the control 77. For example, if the armaturevoltage rheostat 31 is maintained at a constant position and thetemperature of the web (or oven) appears to be rising, the operatorwould control the motor 75 so as to slightly lower the dancer roll 40.This embodiment is relatively unrefined as far as automatic control isconcerned. However, it illustrates a method of making temperature changevery highly responsive to change in the position of the dancer roll.With lowering of the dancer roll, the length of web exposed in the ovenis decreased while simultaneously the length of web exposed in thecooling tower is increased. It may be desirable in some installations toreverse the order of the heat cooling towers, making the cooling towerprecede the heating tower. It will be understood that this principle maybe employed in any of the previously described automatically controlledinstallations.

While all the above specific examples of the invention have employedsimilar ovens and similar dancer arrangements, almost unlimitedalternatives are possible. In FIGURE 5, for example, is schematicallyshown a horizontal oven 218 through which a Web or strand 210 is passed.The web is guided by the idlers 211 and 212 outside the oven and by thefixed idler 213 Within the oven. A pair of dancers 240 and 241 aremounted for pivoting movement around a common axis in the mannerillustrated in the figure. It will be seen that in the dotted lineposition the web or strand has a somewhat increased path of travelthrough the oven. &1ch an arrangement is obviously suitable for only anarrow range of strip speed at a given oven temperature, but within suchrange this arrangement enables fine strip temperature control to beachieved. If there is a roughly linear or planar heat source 220 withinthe oven, the arrangement preferably is such that as the web path islengthened, spacing from the heat source diminishes, the two variablesthus affecting web temperature in the same direction.

In FIGURE 6 is shown another example of an oven and dancer arrangement.Here the web 314 is guided by the idlers 311 and 3 12 outside the oven318 and by the fixed idler 313 Within the oven. A dancer 340 is mountedfor reciprocating movement to vary the length of web within the oven inthe manner indicated in the drawing.

The above description of the invention should make it apparent that theinvention may be embodied in many different specific strip processingset-ups. Disclosure of the invention will suggest to the art manypossibilities for specific installations which are tailored toparticular conditions and operating requirements. The scope of the in- 8vention is, therefore, not limittd to details of the embodimentsdescribed above, but is to be defined by the claims set forth below. Inthe claims it is to be understood that the term roll embraces pulleysand sheaves, cylindrical bars and tubes and other equivalent elements.

This application is a divisional application with respect to ourcopending application Serial No. 456,691, filed September 17,' 1954, nowPatent No. 2,837,834, issued JunelO, 1958.

What is claimed is:

1. Strip treating apparatus comprising a heating chamber having heatingmeans combined therewith, input guide means to guide strip material tosaid heating chamber, output guide means to guide strip material fromsaid heating chamber, other guide means intermediate said input andoutput guide means and comprising dancer guide means, means fortranslatably mounting said dancer guide means for translation withinsaid heating chamber and through a continuous range therein to vary thelength of strip material within the heating chamber over a continuousrange, means to sense the strip tem perature which results from exposureof the strip to heat supplied within said heating chamber by saidheating means, and means responsive to said sensing means to actuatesaid mounting means so as to translate said dancer guide means to varythe length of strip material within the heating chamber as an inversecontinuous function of indicated strip temperature.

2.. Strip treating apparatus comprising a heating chamber having heatingmeans combined therewith, input guide means to guide strip material tosaid heating chamber, output guide means to guide strip material fromsaid heating chamber, other guide means intermediate said input andoutput guide means and comprising dancer guide means, means fortranslatably mounting said dancer guide means for translation fromwithout said heating chamber to within said heating chamber and througha continuous range therein to vary the length of strip material withinthe heating chamber over a continuous range starting from zero, means tosense the strip temperature which results from exposure of the strip toheat supplied within said heating chamber by said heating means, andmeans responsive to said sensing means to actuate said mounting means soas to translate said dancer guide means to vary the length of stripmaterial within the heating chamber as an inverse continuous function ofindicated strip temperature over a continuous range starting from zero.

References Cited in the file of this patent UNITED STATES PATENTS1,467,106 De Moos Sept. 4, 1923 2,092,657 Smith Sept. 7, 1937 2,501,537Parkes Mar. 21, 1950 2,872,173 Munker Feb. 3, 1959

